The present invention relates to surgical knives and particularly to knives used in ophthalmic surgery.
For many years, the predominant method of treating a diseased lens is to remove the diseased lens and replace it with an intraocular lens ("IOL"). Two surgical procedures are preferred for removing the diseased lens: extracapsular cataract extraction and phacoemulsification. Extracapsular cataract extraction involves removing the lens in a relatively intact condition by use of a vectus or similar surgical instrument. Phacoemulsification involves contacting the lens with the vibrating cutting tip of an ultrasonically driven surgical handpiece to emulsify the lens, thereby allowing the emulsified lens to be aspirated from the eye. Although extracapsular cataract extraction has been the preferred surgical technique, phacoemulsification has become increasingly popular, in part because the cutting tip of the ultrasonic handpiece requires only a relatively small (approximately 3 millimeter) tunnel incision.
A typical IOL comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL within the capsular bag. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA), polycarbonate and acrylics, and it may be hard, relatively flexible or even fully deformable so that the IOL can be rolled or folded prior to insertion. The haptics generally are made from some resilient material, such as polypropylene or PMMA and are generally attached to the optic at the 9 o'clock and 3 o'clock positions. IOL's may be characterized as either "one-piece" or "multi-piece." With one-piece IOL's, the haptic and the optic are formed integrally as a blank and the IOL is then milled or lathed to the desired shape and configuration. The multi-piece IOL's are formed either by attaching the haptic to a pre-formed optic or by molding the optic around the proximal end of the haptic.
The diameter of the optic varies depending on the design of the IOL, but an optic diameter of around 5 millimeters (mm) is most common. Although some IOL's are made from a foldable material, allowing the IOL to be inserted through the typical 3 mm incision used with phacoemulsification, in general, the incision must be enlarged after the aspiration of the cataractous lens to allow the IOL to be implanted. Prior to the present invention, surgeons typically used two separate surgical knives, one with a blade width of approximately 3.2 mm for making the initial incision, and a second knife with a blade width of approximately 5.2 mm for widening the initial incision to permit IOL insertion. While the use of two separate knives works well, it results in added expense and time in purchasing, inventorying and, in the case of reusable knives, sterilizing two different knives.
Accordingly, a need continues to exist for a surgical knife that will precisely cut both the initial small incision needed for the ultrasonic cutting tip and the wider IOL insertion incision used in phacoemulsification.